It would be wonderful if patients who need a blood stem cell transplant could ask any willing relative or friend to be their stem cell donor. Unfortunately, it’s not that simple. In order for the transplant to be successful, the patient and donor must have similar genetic markers on their white blood cells.
What Are They Matching?
On the surface of your cells lie sets of proteins. Like a fingerprint, these proteins enable your immune system to distinguish between cells that belong in your body and cells that do not.
If your immune system encounters a cell with the wrong "fingerprint", it orchestrates an attack to destroy it.
Several different proteins on the surface of white blood cells called human leukocyte antigens (HLA) play an important role in stem cell transplantation. Your donor’s HLA type needs to match yours as closely as possible.
Finding a Related Donor
Typically, a patient’s siblings are tested first to determine if they inherited the same HLA proteins from each parent as the patient. The HLA test is painless and requires only a blood sample or a swab of the inside of the donor’s cheeks.
You inherit two sets of HLA proteins from your biological parents: one set from your mother and the second set from your father.
Each of your siblings who has the same two biological parents as the you has a 25% chance of being a ‘perfect’ match' . A perfect match means that the HLA proteins are very similar to yours.
If none of your siblings is a perfect match, your transplant team may suggest a haploidentical transplant. A haploidentical transplant is a transplant using cells from a related donor who only half matches your HLA type. Your biological parents or children are a half-match for you. Many centers are now successfully using haploidentical transplants, which has expanded the number of patients who can undergo a transplant.
Click here to learn more about being a related stem cell donor.
Finding an Unrelated Donor
In the United States, NMDP® (formerly Be The Match®) coordinates the recruitment of unrelated donors. Patients can access more than 41 million potential adult stem cell donors and 800,000 cord blood units through the registry.
- Your doctor can do a preliminary search of the NMDP registry to assess the likelihood of finding a donor for you.
- Donors with the same ethnic background as you are more likely to match you than those from a different ethnic background.
- If potential donors are identified in the preliminary search, the transplant center may then request a formal search.
Once the best donor is identified, he or she will receive extensive counseling by an NMDP representative before giving final consent to donate. Potential donors undergo a complete medical evaluation to ensure they are healthy enough to donate and don’t have any medical problems that could pose a risk to you or themselves.
Click here to learn more about being an unrelated stem cell donor.
Finding a Cord Blood Donor
A transplant using blood stem cells previously collected from a baby's placenta and umbilical cord after birth and stored in a cord blood bank is an option for some patients. Cord blood units do not need to match your HLA type as closely as bone marrow or peripheral blood stem cells. They can also be made available more quickly for transplant, since they have already been collected and stored for later use. However, the number of stem cells in cord blood is less than would be collected from an adult donor. This can increase the time it takes for the cells to begin producing enough healthy blood cells to protect you against infection.
Your doctor can search the NMDP® registry for cord blood donors.
If More Than One Donor is Found
If more than one potential donor is available, several other factors will help your doctor determine the best donor for you.
- Younger donors are usually preferred over older donors.
- Donors who have not been exposed to cytomegalovirus (CMV) are preferable if you, too, have not been exposed to CMV
- Some studies suggest that gender is important. Male patients transplanted with cells from a female, especially one who bore children, appear to have a higher risk of developing a complication after transplant called chronic GVHD
